Phase comparison object locating system



Aug. 26, 1952 BLEWETT 2,608,683

' PHASE COMPARISON OBJECT LOCATING SYSTEM Original Filed Oct. 28, 1943 2 SHEETS-SHEET 2 Fig.3.

[IP07 I Inv'emtor': John Blewett,

His Attorney.

Patented Aug. 26, 1952 1 PHASE coMPARIsoN OBJECTVLOCATING" SYSTEM John P. Blewett, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Original application October 28, 1943, Serial No. 508,024, now Patent No. 2,467,361, dated April 12, 1949. Divided and this application Decemher 29, 1945, Serial No. 638,381

J The present invention relates to radio locating equipment utilizing the comparison of echoes arriving at spaced receiving antennas to determine the direction'of the reflecting object.

This application is a division of my application; Serial No. 508,024, filed October 28, 1943, now Patent 2,467,361, issuedApril 12, 1949, and assigned to the assignee of this application.

An object of my invention is to provide improved echo comparison circuits and equipment for utilizing the circuits to increase the rate at .which information can (be obtained.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further hjects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a diagram of locating equipment embodying my invention; Figs. 2 and 3 are diagrams of phase comparators, and Figs. 4

and 5 are diagrams of ratio circuits.

Referring to Fig. 1 of the drawings there is shown a parabolic cylinder reflector i fixed at an angle of 45 to a vertical pedestal 2 rotated by a motor 3. Spaced apart along the focal line of the reflector are antennas 4, 5, and 6, the antenna 5 at the center being connected to a pulse transmitter I so as to transmit periodic pulses of radio waves each being directed by the reflector in a fan-shaped beam having a width approximately 90.

During the intervals between the transmitted pulses, echoes or reflections from objects located in'the path of the. transmitted waves arrive at the antennas 4 and 6 at times dependent upon the range of thereflecting objects and with a relative phase dependentupon the angular direction of the reflecting objects with respect to the orientation of the antenna system. Since the receivi ng antennas 4 and 6 are correspondingly oriented within the common reflector I, their planes of maximum directivity are coincident with each other and with the plane of symmetry of the reflector l. Therefore, the phase relation between the pulse voltages received at the antenna 4 and 6 from a given reflecting object is a direct function of the angular displacement of that object from. the direction of maximum in- 5 Claims. (CL 343-11) tensity of the receiving antennas, i. e., a line or axis in said plane at right angles to the longiand 6.

g 2' equipment with this line, 'which'may'be called the center line of the plane of the beam, at an elevation of 45, reflections are received from objects at elevations of from 0 to so that the whole sky is scanned during each rotation of the pedestal. Theuse of phase comparison to determine the elevation of the reflecting objects increases the rate at which information can be obtained. a a 1 a In the illustrated equipment, the information is presented on the viewing screens 8 and 9 of cathode ray tubes I0, I I, azimuth and range being presented on the viewing screen 8 and azimuth and elevation being presented on the viewing screen 9.

The map-like presentation on the viewing screen 8 is. obtained from the signal picked up by antenna 6, which is fed through a receiverftZ to'the grid l3 of the cathode ray tube 10. Around the throat of thecathode ray tube is a deflection coil I4 fed by a saw-tooth sweep circuit [5 keyed by the transmitter so as to have a current increasing linearly from a minimum at the end of each transmitted pulse to a maximum immediately prior to a succeeding pulse. The current flowing in the coil M'causes a radial deflection of the beam of the cathode ray tube starting at the center with each transmitted pulse. The coil l4 isrotated by the motor 3 synchronously with the pedestal 2 so the deflecting axis corresponds to the azimuth of the fan-shaped beam transmitted from the antenna 5. [The radial trace on the viewing screen of the cathode ray tube corresponds to the azimuth of the re-' 35 'flecting objects and the modulation of the trace by the'echoes produces spots at a. distance from the center viewing screen corresponding to the rangeof the objects. v

The azimuth and elevation of the reflectingobjects, presented on the viewing screen 9, are obtained by applying the echo signal from receiver E2 to the grid [6 to modulate the beam of the cathoderay tube I I; The beam is deflected horizontally in accordance with the azimuthof the reflecting objects by horizontal deflection plates lfia excited from a potentiometer l'l rotated synchronously with the pedestal 2. The beam is deflected vertically in accordance with the elevation of the reflection of objects by vertical deflection plates I6b excited from circuits hereinafter dscribed, by voltages dependent upon the relative phase of echoes arriving at the antennas 4 In the phase comparisoncircuits, the echosi'gnals from the antennas 4 and 6 are heterodyned against a common local oscillator [8 in converters l9 and to produce an intermediate frequency:- of 30. .=.-megacyc1es.:- ::Because of. the heterodynin'g against a: common-local oscillator, the phase difference between the echo signals is preserved at the intermediate frequency.

plates H. In accordance .withvvusual practicein.

phase comparison, a 90 'phase shift}. indicated at 25, is effected in the relative phase of the voltages prior to the phase comparison. The pur- The. output of IF amplifiers 2| and 22 is fed through" a phase comparator 23 and'aratio circuit 24, i both hereinafter described, to the deflection 'pose of the ratio circuit isztomake thephaseLdetermination independent "of .varlationsti in" the r magnitudes of the voltages fed to the phase. comparator. This takes care of both the effects of ,thaequationbecomes In the apparatus shown, E1 will be very nearly izequali toi-Ezz andno'. substantial error arises if the equation is rewritten as Voltage-atterminal 45 2E E sin 6 Vo1tage a t terminal 50 2E E One of the advantages of the phase comparison circuitiof Fig. 2. is that the input and output circuits cam.be.:gr'ounded without introducing errors sinfi (1) dueitoistray capacities. This is particularly imfading which causes both voltages to fluctuate in unison, and of unbalance in the receiving channels, whichafiectsone, voltage; more. .than the :other. =rw- 1 I .r-In thephase comparator-shown in Fig; 2,..the -output-: of the (IF amplifiers 2 I: and:.:22 is Ted-to input (transformers 126 and lfl v havingtgrounded primary windings 28'. and i 29 a and. grounded secondary windings 30a, 30b and 3| a,-.3 l b.- Both ptherprimary"amt-secondary circuits are tuned by shunt condensers 32, 33, 34, to the frequency of: thevoltages towbe: compared (30 megacycles) F 5 and are: loaded by shunt-resistances :36, 31,1 38, 39 'ftospassza -band ofv about 2 megacycles. This-per- 'mitsfthea;comparison 0f pulse.-.voltagessuch as :tliaechoesi: from remot objects.

The secondaries 30a, 3| :1 and 30b, 3| 1) areiconznected inzseries, with .theinstantaneous voltages respectivelysbucking and'said-ing as. indicated by thezvvoltage: arrows on the qdrawing,. by..pairs.of

mt monnected in reverse polarity to, ground:'-

through. condensers 1 43-, -44 which accordingly. are charged: to: voltages :ofv opposite. polarity-each proportionaLtm-the square; of thesum or the difaferencevvoltageas The voltage between terminal -45;anchgroundsisg proportional to the-product .0!

the. magnitudes of the tw voltages to. be. com- -.-P3I8difl1'ld thesine of the phase displacement be-- tweenethe avoltagesplus some higher. order .terms .which are negligible if the phase displacementis .-sma1l...-.-'I"hese higherorder terms are duelto the .wariation I offthe detectors. 41' and" 42- fromv a.- true square-law.

By using another pair of..;diodes..4B and 41,

withthe. same polarity. with respect to each. other, D connected; to. ground through condensers. .48. and

.49,1'thecondensers.'are charged to the squareof the; respective =sum. anddifference voltages; At terminal .50 appears a voltage proportional to .theisumjof the'squares of the. magnitudes of the voltages .120, be compared, plus 5 some negligible f'hi'gher. orderilterms. "111 E1 and Ez'arezthe, mag- "nitr des/of. thevoltages .to be compared and. 0 is thejjphasetdifierence"between thervoltages portantin phase comparison at high frequencies. Theugrounding is. made possible by the connection of each of the pairs of secondaries 30a, 3m and 30b, .3 lb. in a bridge circuit-with. one .01 the pairs of.impedances40.. In Fig. 3 is a modification otthe phasecomparison circuit of Fig. 2 in which pentodes figiz 5 3, 54 have beensubstituted for .theimpedances 40 in the bridge circuits. between the transiormers 26. andl'l and the diodes 41,42, .46, IQT The. in-

stantaneous potentials withv respect..1.to.,.ground.

across the secondary windings 30a, 3011,} I a; and 31b. arethe sameas those indicated at Fig.2and .havefbeen similarly indicated by voltagelarrows on Fig. 3' of the drawing. The secondaries 30a and 3 la are. connectedv respectively .to. .thei gr'ids 5m and. 52a. and an. amplified outputvoltageproportional. to the. sum of. the voltages. to be com.- .pared appears across resistance...55l.. Ifh'ev sec. ondaries 30b. and 31b. are connected'to the control grids of pe'ntodes 53'and 54and.-an=amplified output voltage; proportional to .the difierence of the voltages to be .comparedappears across re,- sistance 56. The, amplifier. outp'uhvoltages', asin the Fig. v2 circuit, arefed throughthe..dlodeldetectors 4|; to. obtain a voltage at. terminal. 45 proportional totheiprodu'ctjof the voltages tobe comparedby the sine. of.,the phaseaanglebetween the voltages. Similarly, from; diode detectors. 46 and. 41 .a voltage. is obtained at terminal in proportional to the sum of the. squares of the Voltages to becompare'd'L Resonant circuits 51 a'nd..58, which include .the diode. capacity,. increase the v:proportion "of the signal. appearing, across. the diodes. The amplifiers 5t, 52;. 53; .54 isolate the detector'circuits fromthe input 'circuitslandalso permit the regaining of .the signal strength sacrificed in the brid'ge'circuits which permit groundingof both the :input and measuringcircuits.

It is obvious; that'unbalance' in :the circuits will cause inaccuracyr- For example, the "amplifier tubes 5|,*52,'53, 54 should have equalfampliflcation; equal'voltages should be indu'cedin the secondari'es 30a, 30b, and 31:1.3112, andfiorf equal input voltages, all of the secondary voltages should be equal and the resonant circuits. at .the transformer windings and at the detectorinput should be tuned to the same-frequency.

Where first and second comparator circuitsare referred to elsewhere herein, it should. be under.-

--fllnoefltheztermsa'orsthis zequation which include smasher the firsticomparatoncncuit includes .iati'arerroriadiolfrequencycomponentsand emce thecircuitxelementsiandcompenem y rterminal jvoltages. V I l The ratiocircuito'f Fig. 4 utilizes the charac- "provide-the voltage at-terminal l5 proportional to the product of thevoltages to be compared and the sine of the phase angle between the voltages, while the second comparator circuitincludes the circuit elements and components necessary to provide the voltage at terminal 50 proportional to thesum of the squares of the voltages to be compared. In the embodiments of the invention illustrated and described herein, the first comparator circuit includes detectors II and 42 and other circuit components associated with these devices and connecting them to. the two receiving antennas. Similarly, the second comparator circuit cting them to the two receiving an- To obviate the necessity of separately measuring the voltages at terminals 45 and 50, ratio circuitsshow n in Figs. 4 and 5 may be used to obtain'a direct measurement of the quotients of the teristics of remote cut-off tubes which over a limited range have 'an output directly proportional toscreen grid voltage and inversely proportional to negative control grid voltage; By using tubes in parallel," this limited. rangecan be extended or made more accurate. The principles are illus- "and 64 are supplied with a negative direct current voltage equal to Ei -i-Ez This voltage appears on terminal 50 of Fig. 3, and terminal 59 of Fig. 3 may be considered connected'directly to terminal 50 of Fig. 4. The grounded terminals 500 and 45a of Fig. 3 may be considered as directly connected to similarly numbered terminals of Fig. 4. The screen grid 66 is supplied with a fixed positive bias potential E0, as from a source 66a, and the screen grid .65 is supplied with the sum of E from source 65a and 2E1E2 sine 0 by a connection from terminal' iiiof Fig. 3 to terminal 45 of Fig. 4. The output voltages across Qre sistances 6i and 62 are then each proportional to the quotient of the respective screen grid voltage divided by the control gridvoltage, and a voltmeter 6811 connected between points 67 and (it will continuously indicate the solution of Equation 1. It is obvious that the ratio circuit may be .used for other voltages It will handle 11-0. 'or pulsed voltages and positive and negative ratios. By the use of the ratio circuit, the

,rneasurement of phase angle can be made sub- :stantially independent of fading or other factors causing fluctuations in magnitude of the voltages to be compared in phase.

The ratio circuit of Fig. which utilizes the characteristics of multivibrators, will handle ratios of D.-C. voltages. This circuit can be operated to indicate the ratio either by the perof the tubes is conducting, one of the voltages to be compared (V1) is applied to the grid resistance 14 and the other voltage (V2) minus the in the embodiments illustrated and described herein includes detectors 46 and 41 and other circuit components associated with these devices "and conne "ages.

first voltage is applied to the grid resistance 13. where V1 and V2 are positive unidirectional volt- Where the ratio circuit is used with a phase comparator such as shown at Fig. 2 or 3, the voltages V1 and V2 are the voltages appearing at the terminals 65 and 50. An ammeter in series with the tube 69 will indicat the ratio of the first voltage to the other voltage. This is based upon the fact that, with identical tubes and RC rid circuits, the time each tube is cut oif is inversely proportional to the grid voltage.

If V1 and V2 are the voltages to be compared, the percentage of time the tube 69 is conductin will be given by the-following equation. w

1 Vr-V1 E 1 1 V, V -V V In the second mode of operation in which the ratio of the voltages is measured by theoutput frequency of the multivibrator, use is made of the fact that with a multivibrator having a positive grid bias the output frequency is linearly proportional to the ratio of the grid voltage to the plate voltage. If V1 is applied to the grid resistances 13 and 74 and V2 is applied to the anodes 15 and 16, the output frequency will be proportional to the ratio V1ZV2- Certain features of the ratio circuits per so are claimed in my copending application Serial No. 638,382, filed December 29, 1945, now Patent 2,553,294, issued May 15, 1951, which is likewise a division of my application Serial No. 508,024, filed October 28, 1943, now Patent 2,467,361.

While I have shown particular embodiments of my invention, it will be understoodthatmany modifications may be made without departing from the spirit thereof, and I contemplate by the appended claims to cover any such modifica tions as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: W 1. In radio locating equipment, means for transmitting pulses of radio waves toward a, re-

mote reflecting object, a pair of directive receiving antennas having a common axis of maximum directivity and adapted to receive echoes from said object, said antennas being spaced apart along an axis transverse to said first axis, whereby the relative phase of echoes received at said antennas is a function of the angle of displacement of said object from said first axis, means comprising a first comparator circuit coupled to both of said angle, means comprising a second comparator circuit coupled to both said antennas for developing a second voltage substantially proportional to the sum of the squares of the magnitudes of said echoes, and means for measuring the ratio of said first and second voltages, thereby to produce a resultant voltage substantially proportional to the sine of said angle.

2. In radio locating equipment, an elongated parabolic antenna reflector, means supporting said reflector for rotation about a selected axis with the longitudinal axis of said reflector intersecting said selected axis at an acute angle, a transmitting antenna positioned within said refiector, means for energizing said antenna to radiate radio waves toward a remote reflecting object, a pair of receiving antennas correspondingly 7 said reflector end speeed eper amg ifiiiifi i'fiflfifiioi'i longitudinal mini-saidre- :e ivine ient nnas; and reflec ed prod-win sub- 1513511533111). eoineidenereceivzine antenna patterns ;1eeeh.-i';.hevii.1g meximum: direetivity in a, plan ithrouzh eeidiongitndinal r flectonex sx, wh reby v.tne lreletive phases-of waves- ;reeeived by. said. reieeiving antennas due. tweehoes from said object is 1" etzdunotienioftheen le ot-displacement of said: object-iwi-th-srespeot: to La. line in said plane at right, angles; .td said longitudinal axi ,,meen .eomnrisingze nheseseomperisenaeircuitsenergized :ixennibeth .said reoeivingentennas .ionmeasnring the reietineenheeeof. said-waves; end-means energized from said circuit for indicating said angle of displacement. H

a A radio locating-equipment comprising means for transmitting pulses of radio waves toward a remote refiecting object, a pair of directiveiiieeeivineentenna Rhevinge common: axis of:

maximum -direetivitvv and-,eda pted :tozieceive r ehoesztroms said ob.ieet,- said antenna/s bein apgrt along-an axis. etrighten les tosa-id .iiesti axisnwhereby the relative phase ofrechoe meceived etpeid-en ennes is .a function or the :zengle 1E.-,:disp1ecementofi saidobject: from said. :iinet X1,i; means; connected to saidentennas ror o tain guga first volta e substantia lypropo tional to the difference in magnitudesazdf said (polices .-meens-eonnected to said antennas. for

de ivineee'seeond vo1tae .subst ntie ly propor fitieneltozth snxnof the ma nitudes oi'se d ohoes, sqnerealaw; 1D$G1 IS1fOrprOYiding detected-volteges r eponsive 130i saidfirst and second voltages,

d ns esnonsiveto theretiozof th -detected --;volt.eges; ,ior producing a voltage. responsive to ithem nitude-oisaidangle.

- 4.;A ;.-radio-f locating equipment comprisin -..m ens.=ior. tretnsmittin ,v pulsesf radi waves tov.vvlan'ri'e .r mote-,-reflQ0ti obieet. a p r of directiveatt eeivingv-entennes vJnetving; .a common axis of maximum directivity andadapted to receive -,eehoes from said. objects, seidantennas being spaced epe trelon enta is ransverse .to-seid -.-first.; axis whereby the relative phase of echoes received.- at; said antennas. is ,a function of th e ele, i'd spl'acement f said o ject-fr m said axi means connected t01-5aid..a.11t8nnars Ior obtaining a fiISt VOIE-age proportional to the dirt- .z-.iereneerin. magn tu s. oft said echo m ans eonnectedttoseidwentennes for deriving "a. second voltage proportionaltto the: .sum. of the magni- .tudes of echoes, square law detectors for said first. and said.. second voltages said detectors pree-thi-rd voltage-substantia y. prop rtiona l e-the. productof the magnitudes (ifsaid received by the. sine of, said angle and a, fourth ,..yo1ta,ge substantially proportional to the sum oflth'e squares of: the mag itudes of saidech es,

. end-electron: dis h rge. device means responsive 8 :tettheexeflo or; said: third and producing-e-z eeultmteneitagea-substmtiellywmpogtidn l-in the-sine otseidenele...

, pamboliet --.entenna reflector,

elong V sunportme. said zzrefledtone on rotation on re .ver

.tieel -exis with the.,.1ongitudine1 ae;is oinseid're- I deem: intersecting: said yer-tiealtexisadt anpi oxi- .metely -e 145?. angle; a trensmittimentmneeentrolls positioned :within.refleeton-m anstor energizing saidsentenne to: rediete-tmdioewe-ves toward :lremetet refle ting object-1e. pair. to! re- .ceivingentenneepositionedmithinseid reflector endspecedeparteiongseid longitudinal reflector naes-isv i nesitesides oi endtepnroximetelyieqnisdistenttirom eeid. trensmittingr.ente.me,.,.seidreantennas. endr fleetor enbe stantially coincident fan-shaped receiving gporoportioneito the smeoftse demnelee 4 norm- :3.

' CITED.

The dollofineretewnees are of. record .in'. the file-9f this pa tenta UNITED YSTATESPATENTS I umb r 'L Neme 1:...l2dte ,042,81 1; Crosby M -v. June-2,1936

"24.111 49: se 7.. .ie

-2-,41 s. ,o94=- ii; 1 1 nenrl yiei'r 2, 8,143 F, Apr, 1,:1eg'1 2427929 Sept. .9, f 1947 2 339 1 on... .6... 1.9518

l ser es... 2,510,692,; 2,523,398

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